The focus of this project is to investigate at the molecular level the structural basis of meiotic chromosome metabolism and segregation in the yeast, Saccharomyces cerevisiae, and to compare it to that of the mouse and related mammalian species. Methods of isolation and identification by light and electron microscopy have been developed for meiosis-specific structures in yeast based on surface spreading techniques combined with immunofluorescence. Whole-mount preparations have been used to demonstrate well- preserved synaptonemal complexes in preparations of yeast meiotic cells, as visualized by both light and electron microscopy. These new methods demonstrate for the first time that meiotic chromosome behavior in yeast closely parallels that in higher eukaryotes. Chromatin condensation and decondensation proceed in step with chromosome pairing, synapsis, and desynapsis. In concert, these events produce the classical stages of leptotene, zygotene, pachytene, and diplotene, demonstrating the utility of yeast as a model system for analysis of chromosome structure and function. A combination of cytological and molecular cloning techniques has demonstrated that the SP011 gene of yeast is required for chromosome pairing and/or synapsis during meiosis. In contrast, chromosome pairing and synapsis proceed apparently normally in a deletion mutant of the RAD52 gene of yeast. Antibodies which recognize the synaptonemal complex in yeast and the mouse are being screened for by these new methods in order to identify protein components of the synaptonemal complex. An antigen associated with paired yeast chromosomes during meiosis has been identified.